In recent years gustatory research has made revolutionary advances at the level of transduction in taste receptor cells. However, the basic organization of the circuits responsible for processing this taste information at the brainstem gustatory relay nucleus has proved particularly difficult to analyze. The overall goal of this application is to better understand how the brainstem taste relay nucleus - the rostral nucleus of the solitary tract (rNST) - encodes, decodes and distributes the information it receives from the oral cavity. Specifically, differences in the morphology, neurophysiology, and synaptology of rNST neurons with known input and projection patterns will be determined. Such information is essential to understand sensory coding mechanisms in rNST because without knowledge of the underlying circuits it is problematic to make conclusions on how sensory information is processed. Most previous investigations of the rNST have relied on recordings from unidentified neurons with unknown roles in gustatory processing. However, there are reports that separate populations of rNST neurons project to either parabrachial or brainstem sites but not both. These separate groups of rNST neurons must have very different functional roles but since prior classifications of rNST neurons were based on whether they respond to lingual stimulation, they have all been uniformly classified as "taste neurons" and assumed to have similar functional roles in taste coding. Thus, the field is using a broad label of "taste neuron" for study of coding in rNST without in fact understanding the basic nature of the neurons and their connections. By specifically labeling rNST neurons with known projection patterns and known afferent input connections new information on rNST circuits will be determined. This approach is based on the hypothesis that different populations of rNST neurons that distribute chemosensory information to different brain areas have different neurobiological properties. The experiments described in this proposal will determine the degree to which the afferent information is transformed as it travels through the rNST and whether these different neuronal subsets have different synaptic characteristics. The results will provide necessary new knowledge for understanding how rNST neurons function in processing information derived from stimulating taste buds. PUBLIC HEALTH RELEVANCE In humans the sense of taste is a significantly factor in the quality of life. Taste stimuli guide food intake and contribute to the pleasure and drive of feeding behavior. Foods that have a pleasurable taste promote consumption and aversive taste leads to rejection. Thus, taste stimuli guide food selection. Recent scientific progress has characterized the receptor proteins and transduction mechanisms at the level of the taste receptor cells but the central nervous system circuits responsible for processing this taste information have received less attention. The overall goal of this application is to better understand the role of the rNST in processing gustatory information. Understanding the neurobiology of taste guided behavior relates to how humans make decisions about food intake which ultimately plays a critical role in human health.